Sensitive relay mechanism



Oct. 5, 1943; w. H. GILLE SENSITIVE RELAY MECHANISM Filed Sept. 4, 1941 3 Sheets-Sheet l TEMPERATURE 3 REsPoNswe rzemswwce =T.R.R.

INVENTOR Willi: H. dillo, BY

ATTORNEY I oczt- 1943- w. H. GlLLE 2,331,182

SENSITIVE RELAY MECHANISM H no INVENTOR Willis H. cAiuQ bm a ML ATTORNEY Oct. 5, 1943.

W. H. GIL-LE smzsmvn RELAY macrumxsu Filed Sept 4, 1941 3 Sheets-Sheet 3 INVENTOR Willis mama BY ATTORNEY Patented Oct. 5, 1943 2,331,182 SENSITIVE RELAY MECHANISM Willis H. Gille, St. Paul, Minn, assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, 1V[ inn., a. corporation of Delaware Application September 4, 1941, Serial No.

Claims.

The present invention relates to sensitive relay mechanism,

of the prior art known to the applicant,

operation has been varied in a Rebalancing conpointer was approaching center position, the motor would be driven too far on its last periodic operation, thus causing the pointer to be deflected in the opposite direction. This overshooting of the control point might be repeated several times in succession, causing the value of the condition being controlled to oscillate about the value which the system was supposed to maintain. This type of oscillatory operation is known as hunting.

It is therefore an object of the present invention to provide a sensitive relay device applicable to condition control systems wherein a condition changingdevice is controlled in accordance with the deflection of a galvanometer pointer, wherein the tendency of the relay device to cause hunting of the system is substantially overcome.

Another object of the invention is to provide a relay device for periodically energizing a motor in accordance with the deflection of a galvanometer pointer, wherein the duration of the period of motor energization is substantially proportional to the deflection of the pointer.

A further object of the present invention is to provide a relay device of the type described wherein the period of motor operation is modulatingly varied in accordance with the pointer position. A still further object is to construct such a device wherein the period of motor operation is varied from zero when the pointer is in center position to continuous motor operation when the pointer is at a position of maximum deflection.

A further object ofrthe present invention is to provide a sensitive relay mechanism of the type described, wherein the period of motor operation pointer deflection over most vanometer pointer.

Other objects and advantages of my invention will become apparent from a-consideration of the attached specification, claims, and drawings, of which t Figure 1 is a diagrammatic sketch of a control system using a sensitive relay mechanism and embodying certain features of my invention,

Figure 2 is a diagrammatic sketch of a difl'erent control system using a modified form of the sensitive relay mechanism of Figure 1, and

Figure 3 is a diagrammatic sketch illustrating V a control system using still another form of my sensitive relay mechanism.

Figure 1 Figure 1 illustrates a system for controlling the supply of heating fluid to a radiator In in accordance with the temperature of the space H in which the radiator i0 is located. A heating fluid which may be, for example, steam or hot water is supplied to the radiator l0 through a supply pipe l2. This fluid, after losing its heat, flows out of the radiator l0 through a return pipe I 3. The supply of fluid to the radiator Iii through the pipe I2 is controlled by a valve M. The valve I4 is operated by a control mechanism generally indicated at 15, which includes a rack l 6 mounted on the valve stem and cooperating with a pinion IT. The pinion l! is driven by a motor 20, through a gear train schematically shown at 2!. The motor 20 is provided with a pair of, windings 22 and 23 which drive The operation the motor in opposite directions.

"I acting through gears minals 3I and 32 by conductors 33 and 34, re-

spectively.

The upper left arm of the bridge, as it appears in the drawing, incudes a fixed resistor 35 and a variable resistor 36. This arm of the bridge connects input terminal 3| wtih an output terminal 31. The variable resistor 36 is provided so that the temperature at which the bridge is balanced may be adjusted.

The upper right arm of the bridge includes a resistance element 40 of nickel or some other material having an appreciable temperature coeflicient of resistance. Although the system will be described as though the element 40 had a positive temperature coefficient, it will be readily apparent to those skilled in the art that an element having a negative temperature coefficient could be used with equal facility. One end of the resistance element 40 is connected to input terminal 31 through a conductor 4|, and the other end of resistance element 40 is con nected to the lower terminal of slidewire resistance I9 through a conductor 42. The upper right arm of the bridge circuit 24 also includes that part of the slidewise resistance I9 between its lower terminal and the point of contact of slider I8 along the resistance I9. This point of contact is numbered 43 in the drawings and serves as one of the output terminals of the bridge circuit 24.

The lower left arm of the bridge includes a fixed resistance 44 connected to input terminal 32 by a conductor 45 and to output terminal 31 by a conductor 46.

The lower right arm of the bridge circuit 26 includes a conductor 50, a fixed resistance a conductor 52, and that portion of the slidewire resistance I9 between its upper terminal and the output terminal 43.

The output circuit of the bridge 24 may be traced from output terminal31 to output terminal 43. This output circuit includes a conductor 53, a coil 54 of a galvanometer generally indicated at 55, and a conductor 56 connected to the slider I8.

The coil 54 is mounted between the poles of a permanent magnet 60. and'is attached to a pointer 6I which is deflected from a neutral is controlled by a bridge circuit I position in accordance with the magnitude and direction of the current flowing through the coil 54. 62, against which it is periodically clamped by a clamping lever 63 pivoted at 64. and operated by a cam 65 acting against a follower 66 on the end of clamping lever 63 at the opposite side of the pivot 64 from the portion which engages the pointer 6|. The follower 66 is biased for engagement with the cam 65 by a spring 61.

The cam 65 is continuously rotated by a motor II and 12, the latter to a shaft 13 on which the cam 65 is also fixed. Also fixed on the shaft 13 are two more cams 14 and 15. The cam 14 acts against a follower 16 mounted on a supporting arm 11, which is mounted on a fixed pivot, as at being attached The pointer 6I moves parallel to -a bar.

biased by a spring so that the follower 16 engages the surface of the cam 14.

Pivotoally mounted, as at 82, on the arm11 is a' switch operator 83. The switch operator 83 is provided with a long vertical extension 84 which is adapted to move transversely to the path of movement of pointer 6|. This switch operator 83 is biased for counter-clockwise rotation about the pivot 82 by a spring 85. Counter-clockwise rotation of the operator 83 with respect to the arm 11 is limited by a stop 65 which extends rearwardly from the operator and engages a portion of the arm 11 when the operator reaches a limiting position.

Rotation of the switch actuating member 83 is prevented by a brake mounted at one end of a leaf spring 9I whose other end is attached to a lever 92, which is pivoted to the arm 11, as at 93. A spring 94 biases the lever 92 for clockwise rotation about the pivot 93 and its movement is limited by a pin and slot connection shown at-81. A long transverse extension of the lever 92 engages the cam 15. Rotation of the cam 15 serves to periodically release the brake 90 and permits rotation of the switch actuating member 83 about the pivot 82. The spring 94 holds extension 95 in engagement with cam 15.

Mounted on the member 83 are a pair oi switch contacts 95 and 91 which selectiv'ely cooperate with stationary contacts 98 and 99 to control the energizing circuits of the motor 20.

The cam 65 which operates the clamping lever 63 is provided with a riser portion I00, a high dwell portion I 0|, a gently sloping dropoff portion I02, and a low dwell portion I03. As the cam 65 rotates clockwise, as indicated by the arrow in the drawing, the clamping lever 63 is held out of engagement with the pointer 6| as long as the follower 66 rides on the high dwell portion IOI of the cam. As the follower 66 moves down the dropoii portion I02, the lever 63 is moved into engagement with the pointer BI by the spring 61. The lever 63 is maintained in engagement with the pointer 6I as long as the follower 66 rides on the low portion I03 of the cam. When the follower 66 rides up the riser portion I00, the lever 63 is moved away from the pointer 61, freeing it.

The cam 14 which reciprocates the arm 11 through the follower 16 comprises a low portion I04, a riser portion I05, a first dropoff portion I06 of relatively short length and steep slope, a second dropofi portion I01 of considerably greater length and gentler slope, and an abrupt dropoff portion I08 connecting the portion I01 with the low portion I04. The arm 11 is at its extreme left-hand position when the follower 16 is engaging the low portion I04. As the follower 16 moves up the riser portion I05, 11 is moved rapidly to the right carrying with it the switch acuating member 83. This moves extension 64 out of the range of movement of pointer BI. As the follower 16 moves down the dropofi. portion I06, the arm 11 is moved rapidly to the left for a short distance. As the follower 16 moves on down the slow dropoff portion I01, the arm 11 continues to move to the left, but at a considerably slower rate. When the follower 16 reaches the abrupt dropofi portion I08, the arm 11 is moved very rapidly to the left until the fol- 8I. The arm 11 is lower 16 engages the low portion I04 of the cam 16. During this last very rapid movement, extenzilon 89 again moves within the range of pointer Cam 15, which operates against the extension 95 of lever 92 and controls the rotation of lever 92 about the pivot 93, is substantially circular except for a small low portion 18. When the extension 95 is engaging the circular portion of the cam I5 the brake 90 is held in engagement with the switch opera-tor 83. When the extension 95 is engaging the low portion 18, the brake 90 is lifted from the switch operator 83, allowing rotation of the latter about its pivot 82. Energy is supplied to the system for operating motors 28 and 10 by a pair of supply lines 51 and 58. Winding 59 of motor 10 is connected directly to lines 51 and 58 then conductors 68 and 69, respectively. Motor 29 is supplied with energy through a transformer IIO having a primary winding II2 connected to the lines 51 and 58, and a secondary winding II I.

Operation of Figure 1 species When the parts are in the position shown in the drawing, the valve I4 is half open, and the slider I8 is therefore in its center position on the slidewire resistance I9. The amount of heating fluid supplied to the radiator I is just sufllcient to keep the space II at the desired temperature and the bridge circuit 24 is therefore balanced. There is no current flowing in the output circuit of the bridge and the pointer 6I is accordingly in its central'position.

The motor 10 is driving the cams 65. I4 and I5 in a clockwise direction. The lever 63 is in a posiiton such that the pointer H is free, since the follower 64 is travelling along the dwell portion IOI of the cam 65. The arm I1 is moving slowly to the left as the cam follower I6 moves down the gently sloping dropoff portion I01. The brake 99 is being maintained in engagement with the switch operator 83 as the extension 95 rides on the circular portion of the cam 15.

As the cams continue to rotate in a clockwise direction, the follower 66 moves down the dropof! portion I02 of the cam 65, thus allowing the spring 61 to move the clamping lever 63 into engagement with the pointer 6 I, clamping it against the bar 62.

Since the bridge is balanced, the pointer will be clamped at its central position. As soon as the pointer BI is clamped, the follower 16 reaches the abrupt dropoif portion I09 of the cam 14 and at approximately the same time the extension 95 of the lever 92 drops into the low portion I8 of the cam 15. Therefore the arm I1 is moved rapidly to its extreme left position and the brake 90 is lifted from the switch operator 83, which turns counter-clockwise about the pivot 82 until its extension 84 engages the clamped pointer 6|. Soon after the extension 84 engages the pointer 6|, thereby determining the position of movable contacts 96 and 91 with respect to the arm 11, the extension 95 moves out of the low portion I8 of cam 15, thereby applying the brake 90 to the switch operator 83, maintaining the contacts 96 and 9'! in the position which was determined by the pointer 6i. After the brake 90 has clamped the switch actuating member 83, the follower I6 engages the riser portion I05 of cam I4, moving the arm 11 with the contacts 96 and 91 mounted thereon rapidly to the right, and out of the range of pointer 6 I. The

. riser I00 on cam 65 then becomes effective to release the clamping lever 63 from engagement with the pointer 6|.

The arrangement of the parts is such that, since the pointer 6| was clamped in a position at the center of its range of movement by the clamping lever 63, the switch actuating member 83 was likewise positioned at the center of its range of movement with respect to the supporting arm 11, by the engagement of extension 84 I with pointer 6|. The switch actuator 83 is maintained in this position with respect to the arm IT by the brake 90. The contacts 98 and 99 are so positioned that when the switch actuator-83 is in its center position and the arm 11 reaches the right-hand end of its stroke, neither of the contacts 98 nor 99 will be engaged by the contacts 96 or 91, respectively. The motor 20 will therefore not be operated and the valve I4 will remain in the position to which it was previously 7 moved.

The contacts 98 and 99 may alternatively be positioned so that both are engaged by contacts 96 and 91, respectively when the actuator 83 is in its center position, as such an arrangement will tery 30 is assumed to be that shown by the legend in the drawings. This causes a flow of current from output terminal 43 through conductor 56, coil 54 of galvanometer 55 and conductor 53, to output terminal 31. This current flowing through the coil 54 causes the pointer 6| to be deflected to the left of its center position. When the pointer 6| is next clamped by the clamping lever 63, it is therefore at-a position to the left of center. When the switch actuator 83 is released by the brake so as to be positioned by the pointer 6|, it rotates to a position displaced in a counterclockwise direction from that shown in the drawings. The switch actuator 83 is held in this new position by the brake 90. In this position of actuator 83 the contact 96 is farther to the right than the contact 91. Accordingly, when the arm 11 is moved to the right by the cam I4, the contact 96 will engage the stationary contact 98.

Engagement of contacts 96 and 98 completes an energizing circuit for winding 22 of motor 20. This circuit may be traced from the upper end of secondary winding III .of transformer IIO through a conductor I I3, switch actuator 83, contacts 96 and 98, a conductor II4, winding 22 of motor 20, and a'conductor II5, to the lower terminal of the secondary winding III. Energization of winding 22 causes 'motor 20 to drive the valve I4 in opening direction. The opening movement of the valve I4 is accompanied by a corresponding upward movement of the slider I8 along the slidewire I9. This increases the portion of slidewire I9 which is connected in series with the temperature responsive resistance element 40 and correspondingly decreases the proportion of slidewire I9 which is connected in series with the fixed resistance 5I. The potential of output terminal 43 is therefore changed in a negative direction and the valve I4 is opened wider so as to increase the heat supplied to the space. As long as the bridge remains unbalanced in the same sense, the system will intermittently operate the motor so as to open the valve and move the slider I8.

When this change has progressed sumciently that the potential of output terminal 43 is equal to that of output terminal 31, the current cc to flow in the output circuit of bridge 24, including the coil 54 of galvanometer 68. The pointer 6| therefore returns to its centerposition, and

when the actuator 83 is next positioned by the I accuse varies to the left of its normal center position, the

a corresponding increase in the resistance of the Y sensitive element 4|), thereby changing the potential of output terminal 63 to a value more negative than that of output terminal 31-. The difierence of potential of the two output ter- 'minals is effective to cause a flow of current in a direction from terminal 31 to terminal 93 through conductor 53, coil 59 of galvanometer 55, aid conductor 56. Since this current flows through the coil 54 in a direction opposite to that produced by a decreased space temperature,

. the pointer 6| will be deflected to the right of its center position. When the switch operator 83 is next positioned by engagement with the clamped pointer 6|, it is therefore displaced in a clockwise direction from the position shown in the drawing. In such a position of the operator 83, the contact 9! will be further to the right than the contact 96. Therefore whenthe arm ll approaches the right-hand end of the span of movement, the contact 91 will engage the contact 99.

Engagement of contacts 91 and 99 completes an energizing circuit for winding 23 of motor 20. This circuit may be traced from the upper terminal of secondary winding I H through conductor ||3, actuator 83, contacts 97 and 99, a conductor H6, winding 23 and conductor H5 to the lower terminal of secondary winding Ill. Energization of winding 23 causes motor 29 to drive valve it in closing direction and to move slider l8 downward along resistance l9. This downward movement of the slider l8 causes a change of potential of output terminal 43 in a positive direction. This movement of the valve l6 and slider l8 continues intermittently as long as the bridge is unbalanced in the same sense. As soon as this change has progressed sufliciently that the potential of the output terminals 31 and 53 are equal, the current ceases to flow through the coil 54, and the pointer 6| returns to its center position. As soon as this takes place, the switch actuator 83 is likewise returned to its center position, and the motor 28 is deenergized. No further movement of the valve M or of the slider l8 takes place until the bridge circuit 28 is again unbalanced.

It will be seen, from the operation previously described, that the position of the switch actuator 83 with respect to the arm ll, is determined by the position of the pointer 6|. It should also be apparent that the position of actuator 83 is not varied in any finite number of steps, but that for any change in th position of pointer 6|, a corresponding change takes place in the position of actuator 83.

Considering for the moment the contact 96, it will be seen that as the positionoi pointer 6| position of contact member 96 is varied to the right of its normal position. The distance of contact 96 from normal position is substantially proportional to the deflection of pointer 6| to the left of its center position. If the deflection of pointer 6| is small, the contact 96 is moved only a short distance to the right of its normal position. As the pointer 6| approaches the left-hand limit of its rang of motion, the contact 96 will approach its limit of motion to the right. This latter limit is determined by engagement of stop 86 on switch actuator 93 with arm 11. If the contact 96 is moved to the right of its normal position, it engages the contact 98 when the arm ll is moved to the rightby the cam 14. Since th contact 98 is flexibly supported, it deflects to the right when engaged by the contact 96. When the contact 96 is moved again toward the left by arm ll, the contact 98 follows it, the contacts remaining in engagement until contact 98 reaches its normal position. The greater the distance of the position oficontact 96 to the right of normal, the greater will be the distance Which the follower 16 must move down the drop-off portion I01 before the contacts 96 and 98 separate. Therefore, the length of time the contacts 96 and 98 remain engaged is dependent upon the distance to which the contact 96 has been moved from its normal position. This in turn depends upon the position of the pointer 6|. Since the rate of movement of arm TI to the left is relatively low, being governed by the small change in radius of the drop-off portion I81 of th cam 14, it may be seen that a small change in the position of pointer 6| and hence in the position of contact 96 will cause a relatively great change in the time of engagement of contacts 96 and 98.

It should therefore be clear that the motor 20 is periodicallyoperated at intervals whose beginnings are uniformly spaced, being governed by the rise portion I of cam it which is rotated by the constant speed motor 78. It should also be clear that the length of each interval is dependent upon the position of the pointer 6|, and that any change in the position of pointer 6| causes a corresponding change in the length of the interval during which the motor is operated. If the pointer 6| remains at its neutral position, however, the motor 28 is not operated at all. Deflections of the pointer 6| in opposite directions from its neutral position cause operation of the motor 20 in opposite directions.

When the pointer 6| is near its center position,

it is desirable that the length of th intervals the result that the valve l4 and slider l8 would continuously oscillate about or hunt, their proper rebalancing position.

Means have therefore been provided in the present invention for reducing the ratio between deflection of pointer 6| and the length of the intervals during which motor 28 is operated, as the pointer 6| approaches its center position. This means comprises the first dropofi portion I66 of the cam 76. This portion 106 causes relatively rapid movement of the arm Il toward the left during the first portion of it movement in that direction from its extreme right-hand position. As a result of this rapid motion to the left when motion in that direction is first started, it will be apparent that if the switch contact 96 is only a very short distance to the right of its normal position, it will be quickly moved away from engagement with the contact 98. The time of engagement of the contacts 96 and 98, and hence the time of operation of motor 20, i therefore proportionately much smaller when its length is determined by the first dropoff portion I03, than when its length is determined by the second relatively slow dropoiT portion I01 of the cam "I4. By thus reducing the length of the intervals of motor operation as the bridge circuit approaches a balanced condition, the length of the last period of motor operation may be made just long enough so that the corresponding movement of the slider I8 will just rebalance the bridge circuit without causing an unbalance in the opposite direction.

In the system described the length of the intervals of motor operation is varied as a continuous function of the deflection of the galvanometer pointer BI. It is true that the ratio of proportionality between these two conditions is changed as the pointer approaches its center position, but the function is nevertheless continuous, as for any change in position of the pointer SI, 8. corresponding change takes place in the length of the interval during which the motor 20 is operated. In other words, the length of the intervals of the motor operation may be said to be modulated in accordance with the position of pointer BI.

Species of Figure 2 In Figure 2 I have shown a control system embodying a modification of my invention in which the intervals of motor operation may be varied from zero when the bridge is balanced to continuous motor operation when the bridge is at a state of maximum unbalance. In this modification I have illustrated a different type of mechanism for reducing the ratio of proportionality between the deflection of the galvanometer pointer and the length of the period of motor operation as the pointer approaches its center position. An additional device "which aids in preventing of the establishment of hunting conditions in the control system is also shown in this figure.

In Fig. 2, parts which are identical with those in the system of Figure 1 have been given the same reference numerals.

Figure 2 shows a radiator I for supplying heat to a space I I. The supply of fluid to the radiator is controlled by a valve I4, which is operated by a control mechanism I5, the operation of which is in turn controlled by the output of a bridge circuit 200, as amplified by a sensitive relay mechanism 20I. The system, except for details of the bridge circuit and the relay mechanism, is similar to that of Figure 1.

The bridge circuit 200 is similar to the bridge circuit 24 of Fig. 1, except that a slidewire resistance 202 is provided, along which a slider 203 is moved by the relay mechanism 20I. The point of contact between slider 203 and slidewire 202 is numbered 204 in the drawings, and serves as one of the output terminals of the bridge circuit 200, corresponding to output terminal 31 in the bridge circuit 24 of Fig. 1.

The upper and lower right arms of the bridge extreme right-hand circuit 200 are the same as the upper and lower right arms respectively of the bridge circuit 24 of Fig. 1.

The upper left arm of the bridge circuit 200 connects input terminal 3| with output terminal 204. This arm includes a fixed resistance 35, a variable resistance 36, a conductor 205, and that portion of the slidewire resistance 202 between its lower terminal and the point of contact 204 of slider 203.

The lower left arm of the bridge circuit 200 connects input terminal 32 with output terminal 204. This arm includes conductor 45, fixed resistance 44, a conductor 206, and that portion of the slidewire resistance 202 between its upper terminal and the point of contact 204 of slider 203.

The output circuit of bridge 200 connects output terminals ,43 and 204. This circuit includes conductor 56, coil 54 of galvanometer 55, and a conductor 201.

In the sensitive relay mechanism 20I, the switch operator 83 carries no contacts such as 96 and 9'! in Figure 1. The switch actuator 83 of Fig. 2 is instead provided with a pair of projections 2I0 and 2! I. A contact supporting member a slip-friction pivot indicated of the sensitive relay mecha- The supporting member 2I2 is provided with a pair of projections 2I4 and 2| 5 which extend towards and are adapted to engage respectively the projections 2I0 and 2H on the switch operator 83. The slider 203 is rigidly attached to the contact supporting member 2 ment therewith? for engagement with the arm U6, and the arm 22I carries a contact 223 for engagement with the contact Zn. The arms 220 and HI are reciprocated towards and away from the supporting member 2I2 by an elliptical cam 224 mounted between the arms 220 and HI on a shaft 225.

The cam shaft 225 is connected with the shaft I3 through suitable gearing 220 and HI are providedwith follower portions 232 and 233 respectively, which are adapted to ride on the surface of the cam 224.

The cam 214 differs from the cam "I4 of Fig. 1 in that the drop-off portions I06 and I01 have been replaced by a high dwell portion 244 of constant radius. The low portion I04, the riser portion I05, and the drop-off portion I 08 correspond exactly to the similar portions of cam I4 The arm 11 is therefore moved to its position by the riser maintained in that position by I6 engages the drop-off por its left position rapidly.

When the follower tion I08, it moves to ation of cam 224. Each engagement Operation of Figure 2 The operation of the system shown in Figure 2 will first be descrlbed as though the slidewire 202 were omitted.; V 7

When the parts are-in the position shown in the drawing, the valve I4 is supplying an amount of heating fluid to the radiator I which is just suficient to keep the space I I at the desired temperature. The bridge circuit 200 is therefore balanced, and the pointer BI is in its central position. The extension 84 has engaged the pointer 6| while the latter was clamped in central position, and the switch operator 83 is therefore also in its central position. When the switch operator 83.is in its central position and the supporting member I1 is moved to th right, the contact supporting member 2I2 is engaged by either projection 2 I 0 or H I and moved to a vertical position so that its lower extremity is midway between the switch arms 220 and 22I. The proportions of the cam 224 are such that when the contact supporting member 2 I 2 is in its mid-position, neither contact 2I5 nor 2Il is engaged by contacts-222 or 223. The motor in the control mechanism I5 is therefore not operated, and the valve I4 is maintained in its present position.

If the temperature in space I I now drops below the value which the system has been set to maintain, the resistance of element 40 decreases, thereby making the potential of output terminal 43 more positive than that of terminal 204. This change in potential causes a current to flow through the output circuit of bridge 200, from terminal 43 to terminal 204, through conductor 56, coil 54, and conductor 201. This current flowing through coil 54 causes deflection of the pointer 6| to the left of its center position. Upon the next engagement of extension 84 with pointer 8|, the switch operator 83 is moved to a position displaced'in a counter-clockwise direction from that shown in the drawing. The projection 2 is thereby moved to the right of its center position, and on the next movement of the supporting arm 11 t0 the right, the projection 2II engages the projection 2I5 on contact supporting member 2I2 so as to move the latter to the right. This positions the contact 2" to the right of center, and when the switch arm 22I is next moved to the left by rotation of the cam 224, contact 2II is engaged by contact 223.

Engagement of contacts 2H and 223 completes an energizing circuit for winding 22 of the motor in the control mechanism I5. This circuit may be traced from the upper secondary terminal of transformer H0 through a conductor 240, switch contact supporting member 2I2, contacts 2H and 223, switch arm 22I, a conductor 24I, winding 22, and a conductor 242 to the lower secondary terminal of transformer H0. Energization of motor winding 22 causes the valve I4 to be driven in opening direction, thereby increasing the supply of heating fluid to the radiator I0. At the same time the slider I8 is driven upward along the slidewire resistance I9, thus making the potential of terminal 43 more negative, and thereby tending to rebalance the bridge circuit 200. As long as the bridge circuit remains unbalanced in the same sense, the contact 2 Il remains to the right of its center position, and the contacts 2 l1 and 223 are intermittently engaged by the operof contacts 2I 'l and 223 cause operation of the motor so as to open the valve wider and move the slider l8 upward so as to rebalance the bridge.

When the slider I8 has moved upward far enough, so that the bridge 200 is rebalanced, the pointer 5| returns to its center position. Upon the next movement of supporting arm 11 to the left, the actuator 83 is positioned by the pointer 6| at the center of its range of movement. As the supporting arm 11 moves back to the right, it engages the contact supporting member 2I2 and moves the latter to its center position, in which position the contacts 2H and 223 can no longer be engaged. The winding 22 is therefore deenergized and no further movement of the valve I4 or of the slider I8 takes place until the bridge circuit 200 again becomes unbalanced.

Now let it be assumed that the temperature of the space I I rises above the value which it is desired to maintain. The increase in temperature causes a corresponding increase in the resistance of the sensitive element 40, thereby changing the potential of output terminal 43 to a value more negative than that of terminal 204. This difference of potential of the two output terminals is I eifective to cause a flow of current in a direction from terminal 204 to terminal 43 through conductor 201, coil 54 of galvanometer 55, and conductor 56. Since this currentfiows through the coil 54 in a direction opposite to that produced by a decrease in space temperature, the pointer 6| is deflected to the ri ht of its center position.

When the switch operator 83 is next positioned by engagement with the clamped pointer GI, it is therefore displaced in a clockwise direction from the position shown in the drawing. In such a position of the operator 83, the projection 2I0 will be moved to the right of its normal position. Therefore, when the arm I1 approaches the right-hand end of its movement, the projection 2I0 engages the projection 2I4 on the contact supporting member 2I2 and rotates the latter in a clockwise direction about its pivot 2I3, thereby causing the contact 2 I6 to move to the left of its normal position. As the switch arm 220 is next moved to the right by operation of the cam 224, the contact 222 will engage contact 2I6.

Engagement of contacts 2l5 and 222 completes an energizing circuit for winding 23 of the control mechanism I5. This circuit may be traced from the upper secondary terminal of transformer H0 through a conductor 240, contact supporting member 2I2, contacts 2I6 and 222, switch arm 220, a conductor 243, winding 23, and a conductor 242 to the lower secondary terminal of transformer H0. Energization of winding 23 causes motor 20 to drive the valve l4 in closing direction and to move the slider I8 downward along resistance I9. This decreases the supply of heating fluid to the radiator I0 and at the same time the movement of the slider l8 causes a change in the potential of output terminal 43 in a positive direction. This movement of the valve I4 and slider l8 continues intermittently as long as the bridge is unbalanced in the same sense. As soon as this movement has continued long enough so that the potential of the output terminals 204 and 43 are equal, the current ceases to flow through the coil 54, and the pointer 6| returns to its center position. As soon as this takes place, the switch actuator 83, and consequently the contact supporting member 2I2 are likewise re- It should be apparent from the foregoing description that the switch contact supporting member 2l2 is modulatingly positioned in accordance with the position of operator 83, and hence in accordance with the position of pointer 6!. The proportions of cam 224 are such that when the member 2l2 is moved to one of its positions of maximum deflection, one of the switch contacts 2I6 or 2!! continuously engages its associated contact 222 or 223. For example, in the case of contacts 2|! and 223, when the contact supporting member H2 is in its position of maximum counterclockwise displacement from the position shown in the drawings, the contact 2 I! is moved so far to the right that by engagement with contact 223 it holds the follower portion 233 of switch arm 22! completely out of engagement with the cam 224, even when the long axis of the ellipse is in line with the follower portion 233. When the contact 2!! is at a position intermediate its central position and its position of extreme deflection to the right, its engagement with contact 223 is periodically interrupted by operation of the cam 224 against the follower 233. Because of the elliptical shape of cam 224, the length of the period of engagement of contacts 223 and 2|! is modulatingly varied in accordance with the deflection of contact 2!! from its normal position. The elliptical shape of cam 224 therefore performs the same function as the slow drop-off portion" of cam 14 in Fig. 1,

The notches 230 and HI of the cam 224 cause the followers 220 and 22! to move more rapidly as they near the center position of contacts H6 and 2!'!. Because of this more rapid movement of the switch arms 220 and 22! near the center positions of contact 2l6 and 2| 1, the length of the periods of engagement of .the contacts are smaller in proportion to the contact deflection when those deflections are very small. In other words, these notches reduce the ratio of proportionality between the length of intervals of motor operation and the displacement of the contacts 2|6 and 2!! from their center position, as those contacts approach that center position. The notches therefore have the same function as the first drop-off portion I06 on the cam 14 in Fig. 1.

Simultaneous engagement of contacts 2l0 and 2!! with contacts 222 and 223 respectively, is prevented by making the notches 230 and MI slightly offset from the ends of the short aids of the ellipse. Since these notches are offset, the

switch arms 220 and 22! do not reach their limits of movement toward the contacts 216 and 2|! simultaneously. Hence, simultaneous engagement of the two switches, due to vibration or other causes, with a consequent energization of both motor windings, is prevented.

The operation of the system of Fig. 2, as thus far described, is entirely analogous to the operation of the system shown in Fig. l. The control mechanism I is operated at equally spaced intervals and the length of each interval is determined by the magnitude of the deflection of pointer B! from its central position. The length of these intervals is modulated from zero when the pointer is in its central position to continuous motor operation when the pointer is at a position of maximum deflection.

The operation of the control system of Fig. 2, with the slidewire resistance 202 included will now be described, Assume that the bridge circuit 200 is balanced and that the supply of Winding 22 in control mechanism l5. This causes 15 the temperature decrease.

movement of the slider l8 upwardly so that the resistance between terminal 43 and input terminal 3| is increased, thereby balancing the change in resistance of the sensitive element 40 due to At the same time, however, due to the counterclockwise movement of the supporting member 2l2, the slider 203 will be moved upwardly along the slidewire resistance 202. This will tend to make the potentialof output terminal 204 more negative, and hence will tend to cause a flow of current in the output circuit of bridge 200 in a direction from output terminal 43 to output terminal 204. This current flow is in the same direction as that caused by the initial unbalancing of the bridge due to the decrease in resistance of sensitive element 40. The initial effect of the resistance slidewire 202 upon an unbalancing of the bridge, is therefore to increase that unbalance. The resistance 202 is however lower in value and hence has a smaller effect upon the bridge circuit than the balancing resistance 19. Therefore as movement of slider I8 along slidewire I9 continues in response to the unbalance of the bridge, the rebalancing effect of slidewire l9 overcomes the unbalancing effects of the sensitive resistance element and the slidewire 202, and the current in the' output circuit of the bridge begins to decrease. As the current in the output circuit de- 40 creases, pointer 6! moves back to the right towards its central position. The contact supporting member M2 is correspondingly moved by the relay mechanism 20! in a clockwise direction about its pivot 2| 3, so that the slider 203 moves downwardly along the resistance 202. Movement 56 wardly along resistance I9.

of the slider 203 downwardly along the resistance 202 has the same effect on the balance of the bridge circuit as the movement of slider I8 up- Ihe effect of slider 203 is now to aid the rebalancing of the bridge circuit. The rebalancing takes place much more rapidly with both slidewires 202 and i9 adding their rebalancing effect.

It may therefore be seen that the initial effect of slidewire 202 is to exaggerate temporarily any unbalance which occurs, thereby making the system more sensitive to unbalance. As the rebalancing mechanism responds to this exaggerated unbalance, and begins to bring the system again 60 to a'balanced condition, the slidewire 202 operates to make the rebalancing action more rapid. The net effect of the operation of slidewire 202 is therefore to accelerate the operation of the system as a whole, thereby increasing its sensitivity.

In a control system, the presence of a time lag between a call for operation by the controlling element and the response of the controlled element may cause the establishment of the condition known as hunting. Such a lag is inherently present in every condition-responsive control system, since it is necessary that a change in the controlling condition takes place before the system responds. If the response is delayed too long while the condition continues to chan e, the response is apt to be greater than is necessary to.

bring the condition to its desired value. This may cause the condition to change in the opposite direction from the desired value, with the result that the control system, after another delay, causes the condition to change back in the direction of its initial deviation. Any device which will reduce the lag of a control system will oppose its hunting tendency.

In other words, it maybe stated that the hunting tendency of a system may be reduced by introducing a corrective factor which is proportional to the rate of system operation. The unbalancing effect of slidewire 202 on the bridge circuit 200 depends upon the position of slider 204, and hence of supporting member 2|2. The position of the latter member, as previously described, governs the length of the periods of operation of the controlling motor, and hence the rate of system operation. The slidewire 202 therefore introduces a corrective factor proportional to the rate of system operation.

Figure 3 Figure 3 shows a system which is the same as that of Fig. 1 with the exception of the switch contact mechanism operated by the sensitive relay. In Fig. 3 parts which are identical with those in Fig. l have been given the same reference numerals.

The switch operator 83 in Fig. 3 carries a pair of projections 2H] and 2, similar to those on the operator 83 in Fig. 2. These projections 2H? and 2 are adapted to cooperate with projections 250 and 25I respectively on a movable contact carrying member 252. The member 252 is mounted through a slip friction pivotal connection 253 on the extremity of an arm 254 which is pivoted at its lower end 255 to the base of the sensitive relay mechanism 25. The arm 25% is biased for movement to the left by spring 255, and its movement in that direction is limited by a stop 257.

The member 252 carries contact portions 2% and 261, which are adapted for cooperation for stationary contacts 99 and 98 respectively.

Operation of Figure 3 The system shown in Fig. 3 operates as a system in a manner quite similar to that of the system shown in Fig. 1. The particular switching mechanism shown operates however in a manner more analogous to the switching arrangement shown in Fig. 2'.

When the switch operator 83 is displaced in a counter-clockwise direction from the position shown in Fig. 3, its next engagement with the member 252 causes the latter to be likewise displaced in a counter-clockwise direction. This displacement of the member 252 in a counterclockwise direction about the pivot 253 continues until both projections 2!!) and 2H engage the projections 250 and 25l respectively. When both sets of projections are engaged further movement of the arm Tl to the right causes the arm 254i to move also to the right, causing engagement of contact 26! with contact 98.

In a similar manner displacement of operator 83 in a clockwise direction from the position shown in the drawing causes engagement of contact 260 with contact 99. Due to the shape of cam i l driving the arm 77 the duration of the period of contact engagement is modulated in accordance with the position of pointer 6| in the same manner as the modulation described and accuse shown in connection with the operation of the system of Fig. l.

The switching mechanism shown in Fig. 3 has a characteristic similar to that of Fig. 2, namely, that of being able to cause continuous engagement of the switch contacts in response to a maximum deflection of the pointer 6 1. When the operator 83 is positioned at the limit of its movement in either direction, its next engagement with the member 252 will cause rotation of the latter to such an angle that the contact 250 or 261 will engage the stationary contacts 99 or 96, respectively, when the arm 254 is in a vertical position.

It will be seen therefore that the switch mechanism shown in Fig. 3 possesses certain advantages also shown by the more complicated switching mechanism of Fig. 2, but not present in the simple mechanism of Fig. 1.

Although I have shown and described certain modifications of my invention, it will be understood that I do not wish to be limited by the particular system shown and described herein, but only by the scope of the appended claims.

I claim as my invention:

1. In a sensitive relay mechanism, in combination, a control element, means for engaging said control element so as to cause it to perform a control function, said means including an operator element movable along a predetermined path in which said control element lies and a member for supporting said operator element, first means for moving said operator element along said path comprising means for reciprocating said supporting member to move said elements into engagement periodically, and second means for moving said operator along said path comprising means for modulatingly positioning said operator element with respect to said supporting member to vary the duration of said periodical engagements.

2. In a sensitive relay mechanism, in combination, a first control element, means for engaging said first control element so as to cause it to perform a control function, said means including a second control element movable along a predetermined path in which said first control element lies and a member for pivotally supporting said second control element, said member being biased to a first position in which said elements are normally disengaged, first means for moving said second control element along said path comprising means for reciprocating said supporting member to move said elements into engagement periodically, and second means for moving said second control element along said path comprising means for modulatingly positioning said second control element with respect to said supporting member to vary the duration of said periodical engagement, the proportions of said second control element being such that when said supporting member is in said first position and said second control element has been moved by said second means to an extreme position, said elements are continuously engaged.

3. In a sensitive relay mechanism, in combination, a member movable in accordance with the variations of a variable condition, an element for performing a control function, an element for operating said control element, an arm for pivotally supporting said operating element, a brake on said arm for restraining movements of said operating element relative thereto, means for moving said operating element alternat ly into engagement with said member and said control element, means for restraining movement of said member just before and during engagement of said operator element therewith, and means for releasing said brake before engagement of said operator element with said member and for applying said brake after said operator has been positioned relative to said arm by said member.

4. In a sensitive relay mechanism, in combination, an element for performing a control function, an element for operating said control element, an arm for pivotally supporting said operatlng element, means for positioning said oper ating element with. respect to said arm, and means for reciprocating said arm to engage said operating element alternately with said positioning means and said control element, the position of said operating element with respect to said arm determining the time of engagement of said elements, said reciprocating means including means for varying the speed of motion of said arm over different portions of its travel to change the relative effect of certain positions of said operating element on the length of said time of engagement.

5. In a sensitive relay mechanism, in combination, an element for performing a control function, an element for operating said control element, an arm for pivotally supporting said operating element, said operating element having a normal position with respect to said arm, means for moving said operating element from said normal position, and means for reciprocating said arm to engage said operating element alternately with said moving means and said control element, the position of said operating element with respect to said arm determining the period of engagement of said elements in such a manner that the period is increased as the operating element position departs from said normal position, said reciprocating means including means for increasing the speed of said arm at the portion of its travel nearest the control element to decrease the proportion between the period of engagement and the departure of said operating element from normal when said operating element is near said normal position.

6. In a sensitive relay mechanism, in combina tion, a pair of switch arms for performing a control function, switch contact means engageable by said switch arms selectively, said contact means having a normal position, means for modulatingly positioning said contact means in accordance with the variations of a variable condition, means for reciprocating said switch arms toward and away from said contact means, the position of said contact means determining the particular switch arm engaged and the duration of said engagement, said duration being substantially proportional to the distance of the position of the contact means from normal position, said reciprocating means including means for increasing the speed of said switch arms at the point of their travel nearest said contact means so as to reduce said duration of said engagement in proportion to the distance of the contact means from normal when said contact means is near said normal position.

'7. In a sensitive relay mechanism, in combination, switch contact means having a normal position, a pair of spaced switch arms for selectively engaging said contact means, said contact means being positioned between said switch arms, means biasing said switch arms into engagement with said'contact means, means for reciprocating said switch arms toward and away from said contact means, said reciprocating means comprising a single elliptical cam mounted between said arms and constantly rotating, and means for moving said contactmeans along the path of motion of said switch arms, so that the position of said contact means along said path determines the particular switch arm to be engaged with said contact means, and the length of the periods of engagement.

8. In a sensitive relay mechanism, in combination, a slidewire resistance member, operating means including a slider for cooperating with said resistance member and switch contact means, said operating means being mounted for movement as a unit and having a normal position, a pair of spaced switch arms for selectively engaging said contact means, said contact means being positioned between said switch arms, means biasing said switch arms into engagement with said contact means, means for reciprocating said switch arms toward and away from said contact means, said reciprocating mean-s comprising an elliptical cam mounted between said arms and constantly rotating, and means for moving said operating means so that said slider moves along said slidewire and said contact means moves along the path of motion of said switch arms, the position of said contact means along said path determining the particular switch arm to be engaged with said contact means and the length of the periods of engagement.

9. A sensitive condition control system, comprising in combination, a galvanometer including a pointer having a normal position; means for deflecting said pointer in accordance with the variations of a variable condition, condition changing means, means for operating said condition changing means including a motor, switch means for controlling said motor, an operator for said switch means, means for alternately positioning said operator in accordance with the position of said pointer and then engaging said operator and said switch means, and means for varying the duration of such periodical engagements in accordance with the deflection of said pointer,

10. A sensitive condition control system, comprising in combination, a galvanometer including a pointer having a normal position, means for deflecting said pointer in accordance with the variations of a variable condition, condition changing means, means for operating said condition changing means including a motor, switch means for controlling said motor, an operator for said switch means, means for modulatingly positioning said operator in accordance with the position of said pointer, means for periodically engaging said operator and said switch means, and means for varying the duration of such periodical engagements in accordance with the deflection of said pointer, the proportions of said operator being such that upon an extreme deflection of said pointer, said motor is operated continuously.

11. A sensitive condition control system, comprising in combination, a galvanometer including a pointer having a normal position, means for deflecting said pointer including a normally balanced electrical network having a condition responsive element therein, condition changing means, means for operating said condition .changing means including a motor, switch means for controlling said motor, an operator for said switch means, means for modulatingly positioning said operator in accordance with the position of said pointer, and means for periodically engaging said operator and said switch means,

means for varying the duration of such periodical engagements in accordance with the deflection of said pointer, and means for introducing an unbalancing effect in said network proportional to the average rat-e of motor operation, said last-named means comprising a slidewire resistance connected in said network, a slider for cooperation with said resistance, and a connection between said switch operator and said slider for moving said slider along said resistance when said operator is moved.

12. In a sensitive relay mechanism, in combination, switch contact means having a normal position, a pair of spaced switch arms for selectively engaging said contact means, said contact means being positioned between said switch arms, means biasing said switch arms into engagement with said contact means, means for reciprocating said switch arms toward and away from said contact means, said reciprocating means comprising an elliptical cam mounted between said arms and constantly rotating, and means for moving said contact means periodically along the path of motion of said switch arms, said moving means comprising a second cam continuously rotated at a speed twice that of said elliptical cam, said cams being related in time phase so that the position of said contact means is changed when said switch arms are at positions remote from the normal position of said contact means.

13. In a sensitive relay mechanism, in combination, switch contact means having a normal position, a pair of spaced switch arms for selectively engaging said contact means, said contact means being positioned between said switch arms, means biasing said switch arms into engagement with said contact means, means forreciprocating said switch arms toward and away from said contact means, said reciprocating means comprising an elliptical cam mounted between said arms and constantly rotating, and means for moving said contact means along the path of motion of said switch arms, so that the position of said contact means along said path determines the particular switch arm to be engaged with said contact means and the length of said engagement is substantially proportional to the movement of said contact means from said normal position, said cam having a pair of notches displaced slightly in opposite senses from the ends of the short axis of said ellipse, said notches increasing the speed of movement of said switch arms at the end of their travel nearest said contact means, and said displacement preventing simultaneous engagement of said switch arms with said contact means.

14. A control system, comprising in combination, a normally balanced electrical network including a condition responsive impedance, a galvanometer with a pointer having a normal position and connected in said network, said galvanometer pointer being deflected in response to an unbalance of said network, control means, means responsive to pointer deflection for periodically operating said control means, said last- -named means including means for varying the length of the periods of operation as a continuous function of the deflection of said pointer from normal position, said function being such that the ratio of length of period to deflection increases with increasing deflection.

15. In a sensitive relay mechanism, in combination, a member normallymovable in accordance with the variations of a variable condition, a control device to be operated in accordance with said condition, an operator for said control device, means including a reciprocable support for moving said operator between a first position in which it engages said member and is thereby positioned with respect to said support and a second position in which it operatively engages said control device for a period of time dependent upon its position with respect to said support, means for clamping said member just before and during engagement of said member by said operator, brake means for fixing the position of said operator with respect to said support, and means for releasing said'brake means during engagement of said member by said operator.

16. In a sensitive relay mechanism, in combination, a member normally movable in accordance with the variations of a variable condition, a control device to be operated in accordance with said condition, an operator for said control device, means including a reciprocable support for moving said operator between a first position in which it engages said member and is thereby positioned with respect to said support and a second position in which it operatively engages said control device for a period of time dependent upon its position with respect to said support, means for clamping said member, means for operating said clamping means to fig; said member just before and during engagement thereof by said operator and to release said member at all other times, brake means for fixing the position of said operator with respect to said support, and means for releasing said brake means during engagement of said member by said operator.

17. Control apparatus, comprising in combination, a normally balanced electrical network, variable impedance means in said network for producing an unbalance effect therein, a member positioned in accordance with the unbalance of said network, means for rebalancing said network, motor means for driving said rebalancing means, switch means for controlling said motor means, means for periodically operating said switch means, means for varying the duration of said periodical operations in accordance with the position of said member, and variable impedance means operable in accordance with the position of said member for introducing an unbalance effeet in said network proportional to the average rate of motor operation.

18. In combination, a galvanometer having a pointer, control means to be operated in accordance with the deflection of said pointer from a normal position, and means responsive to deflection of said pointer for periodically operating said control means, said last-named means including means for varying the length of the periods of operation as a continuous function of the deflection of said pointer from normal position, said function being such that the ratio of length of period to deflection increases with increasing deflection.

19. In a sensitive relay mechanism, in combination, an element for performing a control function, an element for operating said control element, an arm for pivotally support;v g said operating element, said operating elemei having a normal position with respect to said arm, means for moving said operating element from said normal position, means for reciprocating said arm to engage said operating element alternately with said moving means and said control element, the

position of said operating element with respect to said arm determining the period of engagementof said elements in such a manner that the period is increased as the operating element position departs from said normal position, said reciprocatin means comprising a single cam operated at a constant speed in cooperation with a follower on said arm. and means biasing said arm to engage said follower with said cam, said cam being formed so as to increase the speed of said arm at a the portion of its travel nearest the control element. thereby decreasing the proportion between the period of engagement and the departure of said operating element from normal when said operating element is near said normal position.

20. In a sensitive relay mechanism, in combination, an element for performing a control function, an element for operating said control element, an arm for pivotally supporting said operating element, said operating element having a normal position with respect to said arm, means for moving said operating element from said normal position, means for reciprocating said arm to engage said opera-ting element alternately with said moving means and said control element. the

said arm rapidly away from said control element during the first portion of-its travel in that direction, and a second drop-off portion of greater length and gentler slope for moving said arm slowly away from said control element during the ensuing portion of its travel in that direction so as to increase the speed of said arm at the portion of its travel nearest the control element, thereby decreasing the proportion between the period of engagement and the departure of said operating element from normal when said operating ele ment is near said normal position.

WILLIS H. GILLE. 

